ARM: dts: stm32: use the same 3v3 for SD and DSI nodes on stm32f469-disco

ARM: dts: stm32: use the same 3v3 for SD and DSI nodes on stm32f469-disco

In the board schematic, the power supply for the SD card is the same 3.3
volts used to power the LCD panel and other peripherals. By generalizing
the name of the voltage regulator, it simplifies the device tree and makes
it more readable.

Link: https://www.st.com/en/evaluation-tools/32f469idiscovery.html#cad-resources
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>